Orientation Control of Solution-Processed Organic Semiconductor Crystals to Improve Out-of-Plane Charge Mobility

Xiaoshen Bai, Kai Zong, Jack Ly, Jeremy S. Mehta, Megan Hand, Kaitlyn Molnar, Sangchul Lee, Bart Kahr, Jeffrey M. Mativetsky, Alejandro Briseno, Stephanie S. Lee

Research output: Contribution to journalArticlepeer-review


The crystallization of a series of triisopropylsilylethynyl (TIPS)-derivatized acene-based organic semiconductors drop cast from solution onto substrates was investigated as a function of the size of their conjugated cores. When drop cast onto a substrate, the molecules in TIPS-pentacene crystals adopt a "horizontal" orientation, with the long axis of the pentacene core parallel to the substrate surface. For crystals comprising molecules with dibenzopyrene, anthanthrene, and pyranthrene cores, two-dimensional X-ray diffraction patterns revealed the existence of a second population of crystals adopting a "vertical" molecular orientation with the long axis of the acene core perpendicular to the substrate surface. The ratio of the population of TIPS-pyranthrene crystals with molecules adopting horizontal versus vertical orientations was controlled by varying the surface energy of the underlying substrate. These crystals displayed orientation-dependent linear birefringence and linear dichroism, as observed by differential polarizing optical microscopy. Conductive atomic force microscopy (C-AFM) revealed a 42-fold improvement in out-of-plane hole mobility through crystals adopting the vertical molecular orientation compared to those adopting the horizontal molecular orientation.

Original languageEnglish (US)
Pages (from-to)7571-7578
Number of pages8
JournalChemistry of Materials
Issue number17
StatePublished - Sep 12 2017

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Materials Chemistry


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